Kronfeld played as an openside flanker, and his greatest attribute was considered to be the speed with which he was able to get to breakdowns in play, in order to gain or regain possession of the ball. Josh Kronfield is an alumnus of Aquinas College, Dunedin, and is a grand-nephew of two All Blacks of the 1930s, brothers Dave and Frank Solomon.

In 1990 Kronfeld moved to Dunedin to study physical education at the University of Otago. Here he became involved in the Otago University Rugby Club. After playing one game in 1992, Kronfeld gained a starting position in the Otago team in the National Provincial Championship (NPC) for 1993. Kronfeld would eventually play 69 matches for Otago. He completed his BPhEd degree in 1993.

After the inception of the Super 12 competition in 1996, Kronfeld also played for the Highlanders Super 12 franchise. In total, Kronfeld made 42 appearances for the Highlanders.

He made five appearances in the All Blacks’ 1999 World Cup campaign, which included the game against England and the amazing semi-final with France that took place at Twickenham.

Kronfeld remained a first choice player for Otago, the Highlanders and the All Blacks until 2000. At the end of the 2000 season, after 69 matches for Otago, 42 for the Highlanders in the Super 12 and 56 All Black matches including 54 tests, Kronfeld left New Zealand rugby to take up a lucrative contract with the English club, Leicester. In May 2001 he officially signed with English club Leicester Tigers.

After an injury-hit start to the 2001-02 season Kronfeld recovered well, establishing himself as a regular first-team player. He was an unused replacement as Leicester won the 2002 Heineken Cup Final.[1] He was twice voted by fans Player of the Month, once Zurich Premiership Player of the Month and then named by his Tigers colleagues as their Players' Player of the Season 2002-03.

In 2003, Kronfeld returned to New Zealand, and subsequently retired from first-class rugby.